This invention relates to photometric analysis in general and more particularly to an improved method and apparatus for computation of rates in a photometric analyzer.
In application Ser. No. 499,602 filed Aug. 22, 1974, now abandoned, and assigned to the same assignee as the present invention a completely automated kinetic analyzer is disclosed. This application has now been abandoned and a continuation application Ser. No. 594,951 filed July 10, 1975 has been filed on the subject matter thereof. One of the primary problems in constructing such an analyzer is in providing a method of computing rates of absorbance to provide final outputs in a manner which is accurate and reliable. In addition to making an accurate measurement of rate, means must also be provided to insure that the linearity of the output change from a photometer or the like is within pre-established limits. If such is not done erroneous outputs can result.
Typically in the prior art such measurements have been made by measuring at two points in time and the difference between the two measurement values used as an indication of rate. Since the outputs which are being measured in such a device are subject to noise variations this prior art measurement method can result in large errors. It is possible for example for the one measurement to be taken at a peak and the other measurement to be taken at a valley of the super-impressed noise thereby resulting in an output much in error. Furthermore in prior art apparatus in making a check of linearity and doing what is referred to in the art as a curvature check, pre-established curvature limits have normally been set. These curvature limits are used no matter what the rate being measured turns out to be. Clearly the tolerance for curvature will depend on the rate. That is to say that a curvature which might be excessive for a low rate could be perfectly acceptable for a high rate since such curvature would cause the final result to be only slightly in error. However the allowable curvature for the high rate if applied to a low rate would result in completely unacceptable outputs. Because of this, in the prior art apparatus, the curvature limit has been set on the low side. Consequently many rate measurements which are actually valid must be thrown out because of a rejection based on excessive curvature. This of course raises the time required and the expense of carrying out tests of this nature.
Although the prior art apparatus did reject rate measurements having excessive curvature and possibly suffering from other deficiencies they gave the operator no clear indication of what caused the rejection. A clue as to what caused a bad reaction many times can be helpful in determining whether the apparatus is operating incorrectly or whether some other problem exist.
In view of these various deficiencies the need for an improved computation method and apparatus became evident to the inventors herein.